1. Field of the Invention
The invention relates to an apparatus for liquid treatment of work pieces, and a flow control system for use in such apparatus.
2. Description of Related Art
In the semiconductor industry, semiconductor wafers undergo liquid treatment that may include both wet etching and wet cleaning, wherein the surface area of a spinning wafer to be treated is wetted with a treatment liquid and a layer of the wafer is thereby removed or impurities are thereby carried off. A device for liquid treatment is described in U.S. Pat. No. 4,903,717. In this device the distribution of the liquid on the wafer surface may be assisted by the rotational motion imparted to the wafer.
For current technology nodes in the semiconductor industry, it is widely accepted to manually adjust the flow of a given treatment liquid once at installation/setup time, and thereafter to keep this flow constant during processing wafers. Changing the flow rate requires stopping the machine and performing manual adjustments to needle valves or similar components.
However, future technology nodes will likely need more flexible flow setting capabilities. It would be desirable to allow for two or more different, but constant flows while processing one wafer, each flow rate corresponding to a specific process step. It would also be desirable to allow for flow rates that change steadily from an initial value to a final value, with these values being selected in advance based upon the specific recipe used for wafer processing.
A conventional flow control module 50 for closed-loop control of the volumetric flow of liquid is shown schematically in FIG. 1. An ultrasonic flow meter 52 provides a signal via output interface 54 to controller 56, which in turn outputs a signal to an electrically controlled needle valve 58 so as to adjust the flow rate in accordance with the input received from the flow meter 52.
However, such flow control modules are not well suited for use in processing semiconductor wafers and other processes for treating work pieces that are highly sensitive to particulate contamination, because the mechanically moving parts of the needle valve 58 are a source of such contamination. Moreover, the response time of the needle valve 58 can be slower than is desired for some processes, and the provision of the components in a single module 50 prevents those components from being maintained, repaired or replaced on an individual basis.
Another conventional flow control system for closed-loop control of the volumetric flow of liquid is shown schematically in FIG. 2. A first module 60 contains an ultrasonic flow meter 62 and output interface 64 as described above, with a signal processor 72 being provided in a separate module 70. The signal processor 72 provides its output to a controller 82 contained in a module 80, and this controller 80 provides an output signal to an electro pneumatic converter 84, which in turn controls a pressure regulator 86. Pressure regulator 86 is of the type having a valve chamber delimited by the inner sides of a pair of interconnected diaphragms, on the outer sides of which are upper and lower chambers whose pressures are controlled pneumatically.
While this system is not attended by the particulate contamination associated with the first conventional example, the range of available liquid flow rates is too limited to meet anticipated needs for a variety of work piece processes including impending technology nodes in the semiconductor industry. Moreover, the provision of the electronic controller, pressure regulator and liquid conduit in the same module 80 also limits how the system can be maintained and repaired.